In the art of sheet metal pressing, a type of accessory tooling known as the "progressive die" has been and still is extensively used. Many types of work parts require several press operations such as piercing, shearing, forming, drawing, etc. before becoming a finished work piece. Progressive dies comprise a multiplicity of stations, each capable of performing one of said press operations, which are so arranged that they progressively perform these operations without cutting the work part completely free of the strip stock from which it is being made, until the last operation station is reached. The strip stock which is being fed through the die advances a work part one station for each stroke of the press and while the press ram is up. The popularity of the progressive die is due to the fact that a finished part results from each stroke of the press without having to loose-handle the part from one single operation die to another.
Many work parts have offsets and depressions that require these parts to be lifted up out of lower die element, after the die opens, before the strip stock can be advanced to next station, and to achieve this the strip stock is guided through the die by providing a multiplicity of devices engaging both margins of the stock. Each such device is known as a "stock lifter."It usually consists of a relatively small diameter post vertically projecting from a hole in the lower die element and provided both with a spring to drive the liter member upward as the die opens and also with a stop for apportioning its upward movement. Near the upper end of each stock lifter post is a transverse slot for guidably engaging the margin of the strip stock. It will be apparent that the stock lifter must incorporate a feature for restraining it from turning about its own axis in order that its transverse slot will always be properly directed toward the margin of the stock with which it is to be engaged.
Exemplary of conventional stock lifters is that disclosed in the U.S. Pat. to Kenville et al. No. 2,979,004 which employs a key provision outside of the bore containing each stock lifter assembly for limiting upward travel of each spring empowered lifter and for preventing the stock lifter from rotation about its axis. Conventionally the die steels (working elements of the die) are bolted to a die shoe which serves as an assembly base. The key provision is ordinarily fitted into an individual hole in the die steels while the hole or cavity for spring which functions to raise the stock lifter continues down into die shoe. Such an arrangement has at least three objections. Progressive dies are usually an intricacy of elements crowded into a limited space, and thus any feature which takes up extra room and requires accessibility for assembly and service places an extra burden on the die designer. Moreover, the machine work to make provision for such means is extra labor and cost for the die builder. Some segments of the die steels require periodic top surface grinding, and since integrity of stop surface plane must be maintained these resharpened segments of the die steels must be shimmed up to compensate for stock removed by grinding. This in effect raises the lifter keys, and the stock lifters they serve, mounted in these die steels. Fitting operations on the lifter keys then become necessary to bring the lifter stock slots back down in plane with other lifters in the die.
In view of the above objections, it is apparent that an improved stock lifter is needed in this art and particularly one which is assembled in a single straight hole through the steel and die shoe and takes its vertical location from the die shoe rather thatn die steel, yet is readily removable from top of the lower die member without removing the die from the press. Such an improvement should be advantageous to all major participants in this field of art.